Epitaxial lift-off process with guided etching

ABSTRACT

A method for performing epitaxial lift-off allowing reuse of a III-V substrate to grow III-V devices is presented. A sample is received comprising a growth substrate with a top surface, a sacrificial layer on the top surface, and a device layer on the sacrificial layer. This substrate is supported inside a container and the container is filled with a wet etchant such that the wet etchant progressively etches away the sacrificial layer and the device layer lifts away from the growth substrate. While filling the container with the wet etchant, the sample is supported in the container such that the top surface of the growth substrate is non-parallel with an uppermost surface of the wet etchant. Performed in this manner, the lift-off process requires little individual setup of the sample, and is capable of batch processing and high throughput.

FIELD

The present invention relates generally to the electrical, electronic,and computer arts, and, more particularly, to methods for performingepitaxial lift-off, and devices formed thereby.

BACKGROUND

Gallium arsenide substrates are frequently utilized when forming deviceswith III-V materials because these substrates allow III-V films to begrown epitaxially in a lattice-matched manner and thus with few defects.Nevertheless, gallium arsenide substrates are expensive, and it isfrequently not cost effective to utilize such substrates only one time.Epitaxial lift-off (ELO) is one processing scheme that allows a galliumarsenide substrate to be used several times. In a typical ELO process, athin sacrificial aluminum arsenide layer is grown on a gallium arsenidegrowth substrate, and then several III-V thin films are epitaxiallygrown on the sacrificial aluminum arsenide layer to produce a devicelayer. The device layer is then further processed to form the desireddevices. With the devices formed, reuse of the gallium arsenide growthsubstrate is afforded by selectively etching away the aluminum arsenidesacrificial layer in hydrofluoric acid so as to undercut the devicelayer and allow it to be lifted away. The liberated device layer maythen be re-attached to some other substrate, which need no longer be asubstrate capable of supporting epitaxial III-V growth. The originalgallium arsenide growth substrate is left intact and undamaged, andavailable for reuse.

Nevertheless, despite their promise, ELO processes may suffer fromseveral disadvantages. For example, when etching the sacrificial layerto lift off the device layer from the growth substrate, it is oftennecessary to create curvature in the sample in order to allow areasonable lateral diffusion rate of etchant to the etching front and toprevent the etching from stopping due to the buildup of gaseousbyproducts from the etching process. Such curvature may, for example, beinduced by the use of weights or wax forms. However, these methods ofadding curvature tend to require that each wafer be set up individually;that is, they are manual, single-wafer solutions. Throughput is low, andattention is required during wet etching.

SUMMARY

Embodiments of the invention provide methods for performing ELO withIII-V growth substrates that require less individual setup and providegreater throughput than conventional ELO methodologies.

Aspects of the invention are directed a method for performing ELO. Asample is received comprising a growth substrate with a top surface, asacrificial layer on the top surface, and a device layer on thesacrificial layer. This substrate is supported inside a container, andthe container is filled with a wet etchant such that the wet etchantprogressively etches away the sacrificial layer and the device layerlifts away from the growth substrate. While filling the container withthe wet etchant, the sample is supported in the container such that thetop surface of the growth substrate is non-parallel with an uppermostsurface of the wet etchant.

Moreover, additional aspects of the invention are directed to anelectronic device formed at least in part utilizing the method presentedin the previous paragraph.

Lastly, even additional aspects of the invention are directed toperforming ELO by initially preparing a sample at least in part byreceiving a growth substrate with a top surface, forming a sacrificiallayer on the top surface, and forming a device layer on the sacrificiallayer. This sample is supported inside a container and the container isfilled with a wet etchant such that the wet etchant progressively etchesaway the sacrificial layer and the device layer lifts away from thegrowth substrate. During the filling of the container, the sample issupported in the container such that the top surface of the growthsubstrate is non-parallel with an uppermost surface of the wet etchant.

Techniques of the present invention can provide substantial beneficialtechnical effects. By way of example only and without limitation, one ormore embodiments may provide one or more of the following advantages:

-   -   allows an epitaxial layer to be removed from its original        substrate and transferred to a new one, thereby avoiding the        high cost of III-V devices by reusing the substrates;    -   can be applied in cases where a direct etching of structural        material would have undesirable effects on the layer below; and    -   requires little individual setup of the sample, and is capable        of batch processing and high throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 provides a flow diagram of an exemplary method for performingELO, in accordance with an embodiment of the invention;

FIGS. 2-5 show sectional views of intermediate samples formed whenperforming the FIG. 1 method;

FIGS. 6A and 6B show side-view representations of a lift-off processwhile performing the FIG. 1 method; and

FIG. 7 shows a sectional view of a device layer formed using the FIG. 1method after being mated to a different substrate.

It is to be appreciated that elements in the figures are illustrated forsimplicity and clarity. Common but well-understood elements that may beuseful or necessary in a commercially feasible embodiment may not beshown in order to facilitate a less hindered view of the illustratedembodiments.

DETAILED DESCRIPTION

The present invention will be described with reference to illustrativeembodiments. For this reason, numerous modifications can be made tothese embodiments and the results will still come within the scope ofthe invention. No limitations with respect to the specific embodimentsdescribed herein are intended or should be inferred.

As the term is used herein and in the appended claims, “about” meanswithin plus or minus ten percent. Moreover, “III-V materials” and “III-Vfilms” are materials and films, respectively, that comprise acombination of at least one Group III element (e.g., aluminum (Al),gallium (Ga), and indium (In)) and at least one Group V element (e.g.,nitrogen (N), phosphorous (Ph), arsenic (As), and antimony (Sb)).

FIG. 1 shows a flow diagram of an exemplary method 100, according to anembodiment of the invention for performing ELO while fabricatingsemiconductor devices. FIGS. 2-5, moreover, show sectional views ofintermediate samples formed during this processing. Although the method100 and the structures formed thereby are entirely novel, at least someof the individual processing steps required to implement the method 100may utilize conventional semiconductor fabrication techniques and/orconventional semiconductor fabrication tooling. These techniques andtooling will already be familiar to one having ordinary skill in therelevant arts given the teachings herein. In addition, many of theprocessing steps and tooling used to fabricate semiconductor devices arealso described in a number of readily available publications, including,for example: P. H. Holloway et al., Handbook of Compound Semiconductors:Growth, Processing, Characterization, and Devices, Cambridge UniversityPress, 2008; and R. K. Willardson et al., Processing and Properties ofCompound Semiconductors, Academic Press, 2001, which are both herebyincorporated by reference herein. It is again emphasized that, whilesome individual processing steps are set forth herein, those steps aremerely illustrative and one skilled in the art may be familiar withseveral equally suitable alternatives that would also fall within thescope of the invention.

The exemplary method 100 starts in step 105 with the forming of asacrificial layer 200 on a growth substrate 205, which yields a sample210 shown in FIG. 2. The growth substrate 205 may, for example, comprisea gallium arsenide wafer. The sacrificial layer 200 may, in turn,comprise aluminum arsenide epitaxially grown on the growth substrate205. As will be further detailed below, aluminum arsenide is a goodchoice for the sacrificial layer 200 because it is susceptible to beingetched by hydrofluoric acid at reasonably high etch rates and withextremely good selectivity to other III-V materials.

The epitaxial growth of the sacrificial layer 200 on the growthsubstrate 205 in step 105, and, more generally, the epitaxial growth ofall of the III-V materials described herein, may be performed by, forexample, metal-organic chemical vapor deposition (MOCVD) (also calledmetal-organic vapor phase epitaxy (MOVPE)). During MOCVD, the growthsurface is exposed to vapor-phase metal-organic reactants while beingheated (e.g., to 650° C.). Reactor pressure may be around 100 Torr, andhigh purity nitrogen may be employed as the carrier gas, in one or moreembodiments. Trimethyl gallium, trimethyl aluminum, and trimethyl indiummay be used as Group III precursors, while arsine and phosphine may beused as Group V precursors. Disilane and dimethyl zinc may be utilizedto provide n-type and p-type doping, respectively, although otherdopants are similarly contemplated. Commercial MOCVD reactors areavailable from several sources, including, for example, Thomas Swan &Co., Ltd. (Consett, UK), who manufactures a suitable close-coupledshowerhead cold-wall MOCVD system.

Step 110 involves forming a device layer 215 on the just-depositedsacrificial layer 200 to achieve a sample 220 shown in FIG. 3. Initialprocessing may, for example, include epitaxially growing a stack ofIII-V films. For example, when forming a solar cell, the device layer215 may initially include a film stack comprising n- and p-type galliumarsenide, n- and p-type aluminum gallium arsenide, etc. Film thicknessesmay vary from about 20 nanometers to about two micrometers, although theprecise thicknesses will depend on the application. Again, MOCVD may beused for the epitaxial deposition, with the resultant III-V thin filmslattice-matched to the underlying growth substrate 205. After epitaxy,the device layer 215 may be further processed to form active devices.For example, conventional photolithography, metal evaporation (e.g.,silver, gold, nickel), and reactive ion etching (RIE) may be used topattern the thin films and to create metallic lines and contacts, asdesired.

With the device layer 215 formed in step 110, step 115 involvespreparing the sample 220 for a lift-off process. In the presentembodiment, a support layer 225 is first added to the top of the sample220 such that the support layer 225 is disposed on the top of the devicelayer 215. A resultant sample 230 is shown in FIG. 4. Next, a piece oftape 235 is adhered to the top of the support layer 225, yielding asample 240 shown in FIG. 5.

Both the support layer 225 and the tape 235 aid in handling the sample240 before it is lifted off and handling the device layer 215 afterlift-off. The support layer 225 preferably comprises a material that canwithstand being immersed in hydrofluoric acid without significantetching. It may comprise, for example, a photoresist material such as,but not limited to, polymethyl methacrylate (PMMA) and SU-8. Photoresistmay be deposited by conventional photoresist spin-on techniques.Alternatively, the support layer 225 may comprise metals like copper,gold, and nickel, which are also inert in hydrofluoric acid.

Step 120 includes actually performing the lift-off process. The lift-offprocess involves supporting the sample 240 from FIG. 5 in a containerand then filling the container with a wet etchant to progressively etchaway the sacrificial layer 200 and cause the device layer 215 to liftaway from the growth substrate 205. FIGS. 6A and 6B show side-viewrepresentations of such a lift-off process at two temporal points in theprocess. In FIG. 6A, a container 245 is filled with a wet etchant 250 tothe point where about one-third of the growth substrate 205 of thesample 240 is immersed in the wet etchant 250, while, in FIG. 6B, thecontainer 245 is filled to the point where the growth substrate 205 iscompletely immersed in the wet etchant 250. Notably, while filling thecontainer 245, the growth substrate 205 is supported in the container245 such that a top surface 260 of the growth substrate 205 isnon-parallel with an uppermost surface 255 of the wet etchant 250. Asthe container 245 is filled with the wet etchant 250, the wet etchant250 progressively removes the sacrificial layer 200 and causes thedevice layer 215, the support layer 225, and the tape 235 (hereinafter,collectively the “lift-off layer” 265) to lift away the growth substrate205 and to float on the uppermost surface 255 of the wet etchant 250 asa result of surface tension.

During this processing, the growth substrate 205 is held at an anglerelative to the uppermost surface 255 of the wet etchant 250 via asupport 270 on which the growth substrate 205 rests. The supportincludes an angled surface 272 that is oblique to a bottom of thecontainer 245. As the container 245 is filled with the wet etchant 250,an etch front 275 is created at an edge of the sacrificial layer 200 asthe wet etchant 250 progressively moves up the growth substrate 205. Atthe same time, surface tension causes the lift-off layer 265 to pullaway from the growth substrate 205 and to float to the uppermost surface255 of the wet etchant 250, effectively creating a bend 280 in thelift-off layer 265 at the etch front 275 (FIG. 6A). That is, the bend280 is formed in the device layer 215 (constituting part of the lift-offlayer 265) between a portion of the device layer 215 still disposed onthe sacrificial layer 200 and a portion of the device layer 215 that hasalready lifted away from the growth substrate 205. Once floating at theuppermost surface 255 of the wet etchant 250, the lift-off layer 265adopts an essentially flat orientation due to surface tension (FIG. 6B).

Hydrofluoric acid may etch aluminum arsenide very selectively to otherIII-V materials. In some measurements, for example, etch rates inaluminum oxide are estimated to be over eight orders-of-magnitude higherin aluminum arsenide than they are in III-V materials containingsignificant amounts of gallium. Thus aluminum arsenide is a good choicefor the sacrificial layer 200, and hydrofluoric acid is a good candidatefor use as the wet etchant 250.

Aqueous hydrofluoric acid (HF(aq)) is understood to etch solid aluminumarsenide (AlAs(s)) via two major reactions:

AlAs(s)+3HF(aq)→AlF₃(g)+ASH₃(g)  (1)

AlAs(s)+3HF(aq)+6H₂O→AsH₃(g)+[AlF_(n)(H₂O)_(6-n)]^(3-n)(s)+(3−n)F⁻(aq)+nH₂O.  (2)

In both cases, arsine gas (AsH₃(g)) is a reaction byproduct and maycreate bubbles at the etch front 275 that can inhibit continued etching.Nevertheless, in the present lift-off process, the bend 280 in thelift-off layer 265 at the etch front 275 increases the space at the etchfront 275 between the lift-off layer 265 and the growth substrate 205,increasing the rate of etchant diffusion to the etch front 275 andreducing the chances of bubbles affecting etch rate in this criticalregion. The bend 280 thereby “guides” the etching process and insuresthat the etch can be maintained across the entire growth substrate 205so as to fully detach and float the lift-off layer 265. In fact, thebend 280 benefits the present lift-off process in a manner somewhatsimilar to that in which induced curvature benefits conventional ELOprocesses. But in contrast to ELO processes wherein curvature must beinduced in the sample, ELO in accordance with aspects of the inventiondepends on the natural surface tension of the wet etchant 250 to createthe bend 280. ELO processing in accordance with aspects of the inventiontherefore avoids the individual setup efforts and low throughputsassociated with using curvature-inducing techniques involving suchelements as weights and wax. In fact, the method 100, and, moregenerally, process embodiments within the scope of the invention, lendthemselves easily to batch processing wherein a plurality of samples areprocessed simultaneously in a single container.

While filling the container 245 with the wet etchant 250, the rate offilling the container 245 with the wet etchant 250 (the “fill rate”) ispreferably controlled so that the uppermost surface 255 of the wetetchant 250 does not rise higher than the etch front 275. That is, thecontainer 245 is preferably filled with the wet etchant 250 at a ratethat does not allow the uppermost surface 255 of the wet etchant 250 toclimb higher on the growth substrate 205 than the etch front 275 of thesacrificial layer 200. This assures that the lift-off is well-controlledall the way through the process and the potential for forming more thanone etch front is mitigated. At the same time, it is noted that, inaddition to the fill rate, the angle of the sample 240 also acts todetermine how fast the etch front 275 moves along the growth substrate205, with a larger angle causing the etch front 275 to move more slowlyfor a given fill rate. Accordingly, this angle too becomes a “knob” bywhich to control the lift-off process. In actual reduction to practice,the angle can be modified merely by modifying the angled surface 272 ofthe support 270.

While a sacrificial layer 200 comprising aluminum arsenide is set forthabove, it is reinforced that this choice of materials, like all thespecific material choices described herein, is merely by way ofillustration and other equally suitable material may be utilized. In oneor more alternative embodiments, for example, the sacrificial layer 200may comprise an indium-containing phosphide material (e.g., InGaP,InAlP, InP). Such phosphides have been widely applied as etch stoplayers for the selective etching of arsenide materials, and vice versa,and it is known that these indium-containing phosphides may beselectively etched in hydrochloric acid by a reaction such as:

InXP(s)+HCl(aq)→InCl₃(aq)+XCl₃(aq)+PH₃(g) where X=Al, Ga.  (3)

Additional details concerning performing EPO with anon-hydrofluoric-acid wet etchant are provided in U.S. Pat. No.8,796,120 to Cheng et al. and entitled “High throughput epitaxial liftoff for flexible electronics,” which is hereby incorporated by referenceherein. Thus, there are several alternatives as to the material for thesacrificial layer 200 as well as the wet etchant 250, and thesealternatives would also come within the scope of the invention.

Once the lift-off layer 265 is liberated from the growth substrate 205in step 120, the device layer 215 may be mated with a differentsubstrate, and the support layer 225 and tape 235 removed. The resultsof such additional processing are shown in FIG. 7, which shows asectional view of the device layer 215 mated with a different substrate285. Mating with the different substrate 285 may be accomplished viasurface tension forces or “Van der Waals bonding.” The device layer 215may then be even further processed if so desired. Notably, the differentsubstrate 285 need no longer contain III-V material such as galliumarsenide capable of supporting III-V epitaxy. Rather, the differentsubstrate 285 may be independently optimized for one or more ofdielectric constant, thermal conductivity, cost, weight, radiationhardness, mechanical strength, flexibility, and so forth. Thus, devicesformed by novel ELO processing in accordance with aspects of theinvention may be used in a wide range of applications.

At the same time, after the lift-off process in step 120, the growthsubstrate 205 may be reused to again fabricate III-V devices by simplystarting again at step 105 in the method 100 (as indicated by the returnarrow between step 120 and step 105 in FIG. 1). This recycling cancontinue indefinitely. Accordingly, aspects of the invention provide ahigh yield and high throughput method of performing ELO that allows thegrowth substrate to be reused over and over again.

The method 100 as described above is used in the fabrication ofintegrated circuit chips. The resulting integrated circuit chips can bedistributed by the fabricator in raw wafer form (that is, as a singlewafer that has multiple unpackaged chips), as a bare die, or in apackaged form. In the latter case the chip is mounted in a single chippackage (such as a plastic carrier, with leads that are affixed to amotherboard or other higher level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case, the chip isthen integrated with other chips, discrete circuit elements, and/orother signal processing devices as part of either (a) an intermediateproduct, such as a motherboard, or (b) an end product. The end productcan be any product that includes integrated circuit chips, ranging fromtoys and other low-end applications to advanced computer products havinga display, a keyboard or other input device, and a central processor.These integrated circuits and end products would also fall within thescope of the invention.

In closing, it should again be emphasized that the above-describedembodiments of the invention are intended to be illustrative only. Otherembodiments may, for example, utilize different processing steps andmaterials from those expressly set forth above to achieve embodimentsfalling within the scope of the invention.

All the features disclosed herein may be replaced by alternativefeatures serving the same, equivalent, or similar purposes, unlessexpressly stated otherwise. Thus, unless expressly stated otherwise,each feature disclosed is one example only of a generic series ofequivalent or similar features.

Any element in a claim that does not explicitly state “means for”performing a specified function or “step for” performing a specifiedfunction is not to be interpreted as a “means for” or “step for” clauseas specified in AIA 35 U.S.C. §112(f). In particular, the use of “stepsof” in the claims herein is not intended to invoke the provisions of AIA35 U.S.C. §112(f).

Given the discussion thus far, it will be appreciated that an exemplarymethod for performing epitaxial lift-off includes the steps of:receiving a sample comprising a growth substrate with a top surface, asacrificial layer on the top surface of the growth substrate, and adevice layer on the sacrificial layer; supporting the sample inside acontainer; and filling the container with a wet etchant such that thewet etchant progressively etches away the sacrificial layer and thedevice layer lifts away from the growth substrate. The sample issupported in the container such that the top surface of the growthsubstrate is non-parallel with an uppermost surface of the wet etchantwhile filling the container with the wet etchant.

Given the discussion thus far, it will also be appreciated that, ingeneral terms, an exemplary electronic device is formed at least in partby an epitaxial lift-off method set forth above.

At least a portion of the techniques of the present invention may beimplemented in an integrated circuit. In forming integrated circuits,identical die are typically fabricated in a repeated pattern on asurface of a semiconductor wafer. Each die includes a device describedherein, and may include other structures and/or circuits. The individualdie are cut or diced from the wafer, then packaged as an integratedcircuit. One skilled in the art would know how to dice wafers andpackage die to produce integrated circuits. Any of the exemplarystructures illustrated in the accompanying figures, or portions thereof,may be part of an integrated circuit. Integrated circuits somanufactured are considered part of this invention.

An integrated circuit in accordance with aspects of the presentdisclosure can be employed in essentially any application and/orelectronic system in which it is desirable to avoid the high cost ofIII-V devices by reusing the substrates, or where a direct etching ofstructural material would have undesirable effects on the layer below.Applications that may benefit from the techniques described hereininclude, but are not limited to, the fabrication of solar cells. Systemsincorporating such integrated circuits are considered part of thisinvention. Given the teachings of the present disclosure providedherein, one of ordinary skill in the art will be able to contemplateother implementations and applications of embodiments of the invention.

The illustrations of embodiments of the invention described herein areintended to provide a general understanding of the various embodiments,and they are not intended to serve as a complete description of all theelements and features of apparatus and systems that might make use ofthe circuits and techniques described herein. Many other embodimentswill become apparent to those skilled in the art given the teachingsherein; other embodiments are utilized and derived therefrom, such thatstructural and logical substitutions and changes can be made withoutdeparting from the scope of this disclosure. The drawings are alsomerely representational and are not drawn to scale. Accordingly, thespecification and drawings are to be regarded in an illustrative ratherthan a restrictive sense.

Embodiments of the invention are referred to herein, individually and/orcollectively, by the term “embodiment” merely for convenience andwithout intending to limit the scope of this application to any singleembodiment or inventive concept if more than one is, in fact, shown.Thus, although specific embodiments have been illustrated and describedherein, it should be understood that an arrangement achieving the samepurpose can be substituted for the specific embodiment(s) shown; thatis, this disclosure is intended to cover any and all adaptations orvariations of various embodiments. Combinations of the aboveembodiments, and other embodiments not specifically described herein,will become apparent to those of skill in the art given the teachingsherein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, steps, operations, elements, components, and/or groupsthereof. Terms such as “above” and “below” are used to indicate relativepositioning of elements or structures to each other as opposed torelative elevation.

The corresponding structures, materials, acts, and equivalents of allmeans or step-plus-function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the various embodiments has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the forms disclosed. Many modifications and variations willbe apparent to those of ordinary skill in the art without departing fromthe scope and spirit of the invention. The embodiments were chosen anddescribed in order to best explain the principles of the invention andthe practical application, and to enable others of ordinary skill in theart to understand the various embodiments with various modifications asare suited to the particular use contemplated.

The abstract is provided to comply with 37 C.F.R. §1.72(b), whichrequires an abstract that will allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. In addition, in the foregoing DetailedDescription, it can be seen that various features are grouped togetherin a single embodiment for the purpose of streamlining the disclosure.This method of disclosure is not to be interpreted as reflecting anintention that the claimed embodiments require more features than areexpressly recited in each claim. Rather, as the appended claims reflect,inventive subject matter lies in less than all features of a singleembodiment. Thus the following claims are hereby incorporated into theDetailed Description, with each claim standing on its own as separatelyclaimed subject matter.

Given the teachings of embodiments of the invention provided herein, oneof ordinary skill in the art will be able to contemplate otherimplementations and applications of the techniques of embodiments of theinvention. Although illustrative embodiments of the invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that embodiments of the invention are not limited to thoseprecise embodiments, and that various other changes and modificationsare made therein by one skilled in the art without departing from thescope of the appended claims.

1. A method for performing epitaxial lift-off, the method comprising thesteps of: providing a support structure having an upper surface which isangled relative to a bottom of a container; receiving a samplecomprising: a growth substrate with a top and bottom surface; asacrificial layer on the top surface of the growth substrate; and adevice layer on the sacrificial layer; supporting the sample whereby anentire bottom surface of the growth substrate rests on the upper surfaceof the support structure inside the container; and filling the containerwith a wet etchant such that the wet etchant progressively etches awaythe sacrificial layer and the device layer lifts away from the growthsubstrate; wherein the sample is supported in the container such thatthe top surface of the growth substrate is non-parallel with anuppermost surface of the wet etchant while filling the container withthe wet etchant.
 2. The method of claim 1, wherein the growth substratecomprises a III-V material.
 3. (canceled)
 4. The method of claim 1,wherein the sacrificial layer comprises aluminum arsenide.
 5. The methodof claim 1, wherein the device layer comprises a III-V material that islattice matched to the growth substrate.
 6. The method of claim 22,wherein the support layer comprises polymethyl methacrylate photoresistmaterial.
 7. The method of claim 22, wherein the support layer comprisesat least one of a photoresist and a metal.
 8. The method of claim 22,wherein the sample further comprises tape disposed on an upper surfaceof the support layer.
 9. The method of claim 1, wherein the wet etchantcomprises hydrofluoric acid.
 10. The method of claim 1, wherein thesacrificial layer is characterized by an etch rate in the wet etchantgreater than the etch rate of a remainder of the sample while fillingthe container with the wet etchant.
 11. The method of claim 1, whereinsupporting the sample inside the container comprises supporting thesample on an angled surface oblique to a bottom of the container. 12.The method of claim 1, wherein filling the container with the wetetchant comprises filling the container at a rate that does not allowthe uppermost surface of the wet etchant to climb higher on the growthsubstrate than an etch front of the sacrificial layer.
 13. The method ofclaim 1, wherein the device layer floats on the wet etchant due tosurface tension after lifting away from the growth substrate.
 14. Themethod of claim 1, wherein, while filling the container with the wetetchant, a bend is formed in the device layer between a portion of thedevice layer still disposed on the sacrificial layer and a portion ofthe device layer that has already lifted away from the growth substrate.15. The method of claim 1, further comprising the step of reattachingthe device layer to a different substrate.
 16. The method of claim 1,further comprising the step of reusing the growth substrate in asubsequent epitaxial lift-off process.
 17. A method for performingepitaxial lift-off, the method comprising the steps of: providing asupport structure having an upper surface which is angled relative to abottom of a container; preparing a sample at least in part by: receivinga growth substrate with a top and bottom surface; forming a sacrificiallayer on the top surface of the growth substrate; and forming a devicelayer on the sacrificial layer; supporting the sample whereby an entirebottom surface of the growth substrate rests on the upper surface of thesupport structure inside the container; and filling the container with awet etchant such that the wet etchant progressively etches away thesacrificial layer and the device layer lifts away from the growthsubstrate; wherein the sample is supported in the container such thatthe top surface of the growth substrate is non-parallel with anuppermost surface of the wet etchant while filling the container withthe wet etchant.
 18. The method of claim 17, wherein forming a devicelayer comprises epitaxial growth of a III-V material that is latticematched to the growth substrate.
 19. An electronic device formed atleast in part by an epitaxial lift-off method, the epitaxial lift-offmethod comprising the steps of: providing a support structure having anupper surface which is angled relative to a bottom of a container;receiving a sample comprising: a growth substrate with a top and bottomsurface; a sacrificial layer on the top surface of the growth substrate;and a device layer on the sacrificial layer; supporting the samplewhereby an entire bottom surface of the growth substrate rests on theupper surface of the support structure inside the container; and fillingthe container with a wet etchant such that the wet etchant progressivelyetches away the sacrificial layer, and the device layer lifts away fromthe growth substrate; wherein the sample is supported in the containersuch that the top surface of the growth substrate is non-parallel withan uppermost surface of the wet etchant while filling the container withthe wet etchant.
 20. (canceled)
 21. (canceled)
 22. The method of claim1, wherein the sample further comprises a support layer disposed on anupper surface of the device layer, the support layer comprising amaterial which is inert when immersed in the wet etchant.
 23. The methodof claim 1, wherein, while filling the container with the wet etchant,the bottom surface of the growth substrate is not in contact with thewet etchant.
 24. The method of claim 1, further comprising determininghow fast an etch front moves along the growth substrate at least in partby modifying the upper surface of the support structure.
 25. The methodof claim 24, wherein modifying the upper surface of the supportstructure comprises modifying an angle at which the growth substrate isheld relative to the uppermost surface of the wet etchant when restingon the upper surface of the support structure.